A blood oxygen saturation monitor is an instrument for monitoring blood oxygen saturation. Oxygen saturation is often abbreviated as SaO2 or SpO2. It refers to the degree to which hemoglobin binds to oxygen at a certain oxygen partial pressure, that is, the percentage of oxygen content and oxygen capacity. Usually, it adopts the oxygen saturation of the arteries. People only need to clip on to finger, toe, or earlobe to measure blood oxygen levels. It is an essential device for people with chronic lung or heart conditions, who have to monitor how well oxygen is being sent from the heart and lungs out to the furthest parts of the body.